In the prior art, there are many well-known systems and techniques for wavefront sensing and wavefront phase distortion suppression. Typically the resolution of such systems is rather low. However, the situation is rapidly changing with the upcoming new generation of wavefront phase compensation hardware: liquid crystal and micro-electromechanical system (MEMS) phase spatial light modulators (SLMs) having on the order of 104 to 106 elements. Such resolution is difficult to, achieve with traditional wavefront sensors used in adaptive optics: shearing interferometers, Shack-Hartmann sensors, curvature sensors, etc. In these sensors, the wavefront phase must be reconstructed from its first or second derivatives which requires extensive calculations.
Time-consuming calculations are also the principal obstacle for wavefront sensors based on focal plane techniques: phase retrieval from a set of pupil and focal plane intensity distributions, phase diversity, or Schlieren techniques. For these methods, the dependence of the wavefront sensor output intensity (sensor output image) on phase is nonlinear, and phase reconstruction requires the solution of rather complicated inverse problems.
The problem of phase retrieval from high-resolution sensor data can to some degree be overcome by using a recent adaptive optics control paradigm that utilizes the wavefront sensor output image directly without the preliminary phase reconstruction stage. This approach requires high-resolution opto-electronic feedback system architectures. In these systems, a high-resolution wavefront corrector is interfaced with a wavefront sensor output camera, either directly or through opto-electronic hardware performing basic image processing operations in real-time in a parallel, distributed fashion.
High-resolution adaptive-optic wavefront control and wavefront sensing are complementary problems. When compensating phase distortions with an adaptive system, the phase reconstruction problem is automatically solved as compensation results in the formation of a controlling phase matched to an unknown phase aberration (in the condition of perfect correction). From this viewpoint, high-resolution adaptive-optic systems can be considered and used as a parallel optoelectronic computational means for high-resolution wavefront phase reconstruction and analysis.
Although the phase-contrast technique invented by Frits Zernike in 1935 has been considered as a candidate wavefront sensor for adaptive-optic wavefront control in the past, practical limitations of the conventional Zernike filter have prevented its use in practical adaptive-optic systems, The Zernike filter is a well-known Fourier-domain filtering technique in which a glass slide with a fixed phase-shifting dot placed in the focal plane of a lens is used to phase-shift the zero-order spectral component of a monochromatic input beam relative to the rest of the spectrum. The phase-shifted zero-order component of the input beam then serves as a reference beam, which when superimposed with the other component of the input beam yields an intensity distribution which is a nonlinear functional of the input beam wavefront phase distribution.